1. Field of the Invention
The present invention relates generally to a magnetic storage media system, and particularly to a method and apparatus for detecting the magnetic decoupling of a storage medium from a media system drive motor.
2. Background of the Invention
Magnetic tape is a widely used data storage media. Tape drives and their corresponding tape media are applied to data storage tasks in all levels of computer data storage from personal computers to workstations to mainframes and supercomputers. Much of magnetic tape's popularity is due to the fact that it offers the lowest cost per unit of storage and highest volumetric storage efficiency of all available technologies. Tape products are available in many formats from many vendors in a wide range of cost categories ranging from less than one hundred to many ten's of thousands of dollars.
A magnetic tape drive system may include an elevator mechanism to load and unload the storage media within the tape drive system. For example, a tape drive cartridge elevator may be used to automatically retrieve a cartridge from a tape drive to transfer the cartridge to a slot in a tape cartridge magazine, and vice versa. The tape cartridge elevator may be positioned within the tape storage unit in a manner such that by raising the tape cartridge elevator, the elevator is allowed to unload cartridges from the cartridge reel motor within the storage unit.
A magnetic coupling system is typically used to hold the storage medium onto a cartridge reel motor. In order for the elevator to be able to unload the storage medium, the force of the magnet must be overcome. A known technique used to displace the storage medium from the coupler magnet involves “peeling” or obliquely elevating the storage medium from the magnet using the force of the raising elevator.
A problem encountered in conventional magnetic storage media systems is that large variations may be introduced in the momentum and resultant stopping distances of the elevator mechanism due to unpredictable torque load/friction variations. For example, a ramped voltage force or current is supplied to the elevator in order to raise the elevator from a lowered position together with the storage medium. Once the storage medium is decoupled from the cartridge reel motor, the elevator may experience a large drop in load when the elevator peels the storage medium from the coupler magnet. In an open-loop system (i.e., no feedback), the elevator controller is “blind” to the motion and position of the elevator until the elevator is detected by the elevator up sensor. Thus, the elevator controller may only adapt the voltage or current supplied to the elevator after the elevator up sensor detects the elevator position. However, at this point, it may be too late to control the elevator motion sufficiently enough to provide for smooth operation and predictable stopping distances. As a result, the timing of this load shift in the midst of the open-loop controlled elevator motion is unpredictable, and the elevator motion may become jerky and uneven. Short stopping distances may fail to raise the elevator far enough to hold its upper position, which must then be recovered by a secondary operation. On the other hand, long distances may cause the elevator to slam into its upper hard-stop, requiring the elevator to be stronger and more costly in order to meet the reliability requirements of the storage system.
Thus, it would be advantageous to have an apparatus and method to reduce the large variations in elevator momentum and resultant stopping distances and provide smoother control of the elevator mechanism in a magnetic tape drive system.